John Frum
Tell me your problems
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4000 watt Inverter on 12 V?
- Thread starter Devin82m
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Wow it is difficult finding a decent clamp meter that does both AC/DC and has an inrush feature. The only one I can find that you can't find in stock in the Klein CL900 which is $150 or the CL450 which is $175. The Kaiweets brand only has one that fit that criteria and it's not in stock anywhere. Uni-T has a couple, but one is only 100 amps, which is kind of useless in any large battery systems I could build. So complicated.
Stop thinking in amp-hours. You need to think in watt-hours. A 24V 100Ah battery has the same amount of energy as a 12V 200Ah battery or a 48V 50Ah battery. Amp-hours can only be compared directly between batteries at the same nominal voltage. A Watt-hour is essentially the amp-hour with the voltage multiplied, so you can compare capacities across different battery systems.
You only need the in-rush feature for the ac side.
400 amps dc wouldn't begin to cover the dc in-rush of a 4000 watt inverter.
OK, that helps, how many amps would work?
John Frum
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To measure the in-rush of a fridge 50 amps is probably plenty.
For the ac side you the in-rush of your inverter is not practical to measure.
If you were to make the 12 volt system you've been planning on the largest dc clamp I'm aware of 400 amps so that is just barely big enough.
My Klein cl390 does 400 amps, but I've not really used the in-rush measurement on the dc side.
OK, then it sounds like that Kaiweets may be a good option then. I don't see the point of measuring anything on the DC side since I will use the formulas to make sure I am within the margin.
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Another question, if I put a 1500 watt inverter on a 12 V system but don't draw the full 1500 watts (probably more like 800 or less) from basic electronics like router, modem, laptops, and monitors, will that be too much? I figured a little under 600 watts in my home office for the stuff I use every day. There are other things in the office, but they aren't used every day or I know they are just too much for at such a small system.
I ask because I already have a Samlex 1500 Watt Inverter, a Midnight Solar KID Solar Charge Controller, and 5 315 Watt panels (not setup yet).
I ask because I already have a Samlex 1500 Watt Inverter, a Midnight Solar KID Solar Charge Controller, and 5 315 Watt panels (not setup yet).
That should work fine.
Bud Martin
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Yes you can, I use 12V 3000W inverter in my system even though the load is only around 400W (TV, computer, lights, air cleaner), but I had to use 3000W so my fridge can start up, once it is running , it only draws 200W and it cycle on and off every 20 minutes or so, so my average draw is only 400 ~500W or so.
GXMnow
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The only drawback of using a larger inverter than needed is the cost. There might be a little more power consumed by the inverter at light load, but that difference should be fairly small. A good quality inverter should not be consuming more than about 20 watts when running without a load. When you get to a large low frequency inverter, that might go a little higher, and a cooling fan might pull some as well, but hopefully they use thermal control, so the fan only runs when the unit is getting warm. My cheapo runs the fan all the time, I may put in a thermal switch some day, but it really is just an emergency use unit.
Many years ago, I had a jump starter box with a 17 ah AGM battery. I ended up screwing a 300 watt inverter on the back, and used that thing to run all kinds of stuff for years. About 5 years after I built that, they finally started selling unit like that. Maybe I should have patented my idea back in 1990. When the AMG batter died, it was cheaper to get a whole new jump starter box. And the battery in the new one died in only 2 years. I think I will stuff it full of LFP cells. 4S7P of the 6,000 mah ones they have at Battery Hookup looks like they will fit and push the capacity from 17 AH to 42 AH. The surge current goes to 252 amps. That should start any car I have. And I will change out my ancient 300W modified sine inverter for a 1,000 watt true sine wave one. This is a whole lot smaller scale than you are talking about, but it sure is convenient to have a one hand carry-able power station. Since the AGM battery failed, I have missed having it on hand. Even with my battery backup inverter in the house, I still used that thing often.
Many years ago, I had a jump starter box with a 17 ah AGM battery. I ended up screwing a 300 watt inverter on the back, and used that thing to run all kinds of stuff for years. About 5 years after I built that, they finally started selling unit like that. Maybe I should have patented my idea back in 1990. When the AMG batter died, it was cheaper to get a whole new jump starter box. And the battery in the new one died in only 2 years. I think I will stuff it full of LFP cells. 4S7P of the 6,000 mah ones they have at Battery Hookup looks like they will fit and push the capacity from 17 AH to 42 AH. The surge current goes to 252 amps. That should start any car I have. And I will change out my ancient 300W modified sine inverter for a 1,000 watt true sine wave one. This is a whole lot smaller scale than you are talking about, but it sure is convenient to have a one hand carry-able power station. Since the AGM battery failed, I have missed having it on hand. Even with my battery backup inverter in the house, I still used that thing often.
One reason I ask is because that's what I have already. Also I feel more pressed to use it every day for my home office since Snoobler here on the forums just told me that LFP should not be used as emergency power systems because the batteries are not meant to sit at a high state of charge for long periods of time, they will die out faster. I was originally only going to use this system as a backup power system that may only be used a few times a year based on power outages. I was just going to park it in my home office and keep it on an AC charger and eventually get my 5 315 watt panels out up and hook a couple up to this little backup system. I wasn't aware LFPs are no good for long term storage... I eventually plan on a whole house power system, but that's years down the road.
GXMnow
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Holding any lithium cell at it's maximum voltage for a long time will slowly reduce the cell capacity. A few days is no problem, a few weeks, might do a little, a month or more is getting bad. They are best stored close to 50% state of charge. Almost no degradation, and also very little self discharge. They can stay at 50% charge for several months without a problem. Maybe cycle them a bit every few months to make sure they stay balanced and end up close to 50% again. If you have a power failure, you have that 50% left to run on until you have the sun on the panels to charge it up again. My home backup battery is cycled every day, only holding at my full charge (about 88%) for an hour or so before the system starts feeding power to my house. It then rests at close to 50% all night (up to 9 hours) until it charges again after the sun is up.
Ah, cool, good to know. So is your BMS set to cutoff at 50%?
No
BMS is set for 10V low voltage disconnect as a last line of defense against over discharging your battery.
Use another method of charging to 50%
Ah, I didn't know if some of these programmable BMSs can have other cutoff states than the obvious 10V cuttoff.
I think some of that data is old but could still be valid. Anyways we will find out because I am floating my EVE cells at apx. 3.390 volts. I do plan to cycle them at least monthly.
My application is tied to a UPS and I can't adjust the float voltage. I read somewhere on another forum of someone basically doing the same thing and is floating his cells at 3.4 volts. He said he didn't have any appreciable loss in capacity or something like that.
The sellers who actually test use test jigs capable of testing many cells at a time. I don't know which sellers have them. Cells are supposed to be stored and shipped with a 50% or less SOC. From what I have seen most here have received their cells with a 40% to 50% SOC, as did I.
Interesting. Yeah, that's a tough one, I don't have a ton of money to play around to figure it out. I received my at 3.8v, so fully charged from the Electric Car Part Company (Will's primary suggested Fortune cell dealer).
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